ARTICLES PUBLISHED ONLINE: 24 APRIL 2011 | DOI: 10.1038/NPHYS1983 Controlled near-field enhanced electron acceleration from dielectric nanospheres with intense few-cycle laser fields Sergey Zherebtsov 1 † , Thomas Fennel 2 * † , Jürgen Plenge 3† , Egill Antonsson 3 , Irina Znakovskaya 1 , Adrian Wirth 1 , Oliver Herrwerth 1 , Frederik Süßmann 1 , Christian Peltz 2 , Izhar Ahmad 1 , Sergei A. Trushin 1 , Vladimir Pervak 4 , Stefan Karsch 1,4 , Marc J. J. Vrakking 5,6 , Burkhard Langer 3 , Christina Graf 3 , Mark I. Stockman 1,7 , Ferenc Krausz 1,4 , Eckart Rühl 3 * and Matthias F. Kling 1,8,9 * Collective electron motion in condensed matter typically unfolds on a sub-femtosecond timescale. The well-defined electric field evolution of intense, phase-stable few-cycle laser pulses provides an ideal tool for controlling this motion. The resulting manipulation of local electric fields at nanometre spatial and attosecond temporal scales offers unique spatio-temporal control of ultrafast nonlinear processes at the nanoscale, with important implications for the advancement of nanoelectronics. Here we demonstrate the attosecond control of the collective electron motion and directional emission from isolated dielectric (SiO 2 ) nanoparticles with phase-stabilized few-cycle laser fields. A novel acceleration mechanism leading to the ejection of highly energetic electrons is identified by the comparison of the results to quasi-classical model calculations. The observed lightwave control in nanosized dielectrics has important implications for other material groups, including semiconductors and metals. T he interaction of nanostructured materials with few-cycle laser light is at present attracting significant attention 1–3 . This interest is driven both by the quest for fundamental insight into the real-time many-electron dynamics and a wide range of applications, including ultrafast computation and information storage on the nanoscale 4 , the generation of extreme ultraviolet (XUV) frequency combs 3 , and plasmon-enhanced photoprocesses in femtosecond photochemistry, light detection, and solar energy conversion 5 . Access to the attosecond dynamics of nanostructured materials under laser light at optical frequencies became feasible with the availability of waveform-controlled near single-cycle optical fields 6 and XUV light pulses as short as 80 attoseconds 7,8 . Such light fields have made it possible to study tunnelling of electrons in atomic ionization 9 , valence electron motion in atoms 10 , attosecond photoemission dynamics in solids 11 , and may serve to monitor nanolocalized plasmonic fields with attosecond temporal resolution 12 . The key to applications of nanosystems in the ultrafast regime is the control of nanoscopic electric fields on sub-cycle timescales 12 . A powerful tool to steer electron dynamics on sub-femtosecond timescales is the use of phase-controlled few-cycle laser pulses in the visible 13 , where the electric field evolution is given by E (t ) = E 0 (t )cos(ωt + ϕ), where E 0 (t ) is the amplitude envelope, ω the angular frequency of the carrier wave, and ϕ the carrier- envelope phase (CEP). Waveform-controlled laser fields have been 1 Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching, Germany, 2 Institute of Physics, University of Rostock, Universitätsplatz 3, 18051 Rostock, Germany, 3 Physical Chemistry, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany, 4 Physics Department, Ludwig-Maximilian University, Am Coulombwall 1, 85748 Garching, Germany, 5 Max-Born-Institut, Max-Born Strasse 2A, D-12489 Berlin, Germany, 6 FOM Institute for Atomic and Molecular Physics, Science Park 113, 1098 XG Amsterdam, The Netherlands, 7 Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA, 8 J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA, 9 King Abdullah Institute for Nanotechnology, King Saud University, Riyadh 11451, Saudi Arabia. † These authors contributed equally to this work. *e-mail: thomas.fennel@uni-rostock.de; ruehl@chemie.fu-berlin.de; matthias.kling@mpq.mpg.de. previously used to control the electron emission from atoms 14 and electron localization in molecules 15 . One of the most promising routes to the realization of electronics operating at light wave frequencies 8 arises from applying such waveform-controlled few- cycle light fields to nanoscale systems 16–18 . Recent theoretical work predicts efficient phase control of surface-plasmon driven electron emission from metallic nanofilms, where electrons are accelerated by the locally enhanced evanescent field of laser-induced surface-plasmons 18,19 . Also recollision of elec- trons in strong laser fields was shown to be important for nanosys- tems, for example for high-harmonic generation in clusters 20 and the fragmentation dynamics of C 60 (ref. 21). High-energy electron emission observed recently in medium sized Ag clusters was as- cribed to a rescattering process, where electrons are driven through the cluster by the plasmon-enhanced polarization field 22 . The present work focuses on dielectric nanoparticles in the gas phase and reports a novel phase-sensitive acceleration mechanism relying on electron backscattering from the surface of the nanoparticles in the presence of a dynamical near field. Dielectric nanoparticles were chosen as their spectral response is wide allowing the effec- tive use of the full bandwidth of ultrashort pulses. Furthermore, the larger work function makes it possible to realize tunnelling ionization conditions with relatively low ionization yields up to high intensities, enabling the probing of the dielectric response with only limited interaction between liberated carriers. By imaging NATURE PHYSICS | ADVANCE ONLINE PUBLICATION | www.nature.com/naturephysics 1 © 2011 Macmillan Publishers Limited. All rights reserved.